1. Field of the Invention
The present invention relates to an image processing technique, and, more particularly to a technique for performing color adjustment for images.
2. Description of the Related Art
In recent years, there has been an increasing demand for color print because of colorization of documentation application software (word processor, spread sheet, and rendering software) and spread of the same.
When the color print is performed using such application software, a document may be printed in colors undesirable for a user. In particular, when a corporate mark (a logo) or the like for which accurate colors are indispensable is printed, the mark may be printed in colors slightly deviating from desired colors.
This is caused by a design of color conversion parameters of a printer. The color conversion parameters of the printer are basically designed to print accurate colors. On the other hand, since various figures, characters, and natural images are objects of printing, the color conversion parameters are fine tuned such that, when the respective objects are printed, average users feel that colors are preferable. For example, in many cases, the color conversion parameters are fine tuned to be slightly bright or slight strong in contrast such that preferable colors are obtained. Therefore, slight deviation may occur in colors of the print of the corporate mark requiring accurate colors.
Even when the color conversion parameters are designed to print accurate colors, it is difficult to create the color conversion parameters for accurately printing all colors inputted. An error of colors partially occurs. For example, concerning the corporate mark, every company has different colors of a corporate mark. Thus, although a certain corporate mark can be printed in accurate colors, another corporate mark may be printed in colors deviating from accurate colors. Further, printers have individual differences to some extent, even if color conversion parameters set in a printer in advance are used, it is not always possible to print colors as expected from the color conversion parameters.
Users have different tastes of colors individually. Thus, for example, when a usual red character is printed, a user may feel dissatisfied with red by the color conversion parameters.
As measures for coping with such problems, there is color adjustment processing. FIG. 16 is a diagram for explaining the color adjustment processing. The color adjustment processing is, for example, processing for correcting color conversion parameters stored in a printer such that a print result of desired colors is obtained. First, a color adjustment processing unit 801 reads presently set color conversion parameters from the printer. The color conversion parameters are stored in a color conversion parameter storing unit 802 arranged in the printer. The color adjustment processing unit 801 reads color adjustment image data for correcting the color conversion parameters. This color adjustment image data is usually image data including plural different color patches prepared in advance. These color patches are treated as color data inputted to the printer. The color adjustment processing unit 801 corrects the color conversion parameters to obtain desired colors from this color data. The color conversion parameters corrected are stored in the color conversion parameter storing unit 802 in the printer again.
FIG. 17 is a diagram for explaining color conversion paths for performing color conversion processing for an input image using the color conversion parameters adjusted as described above. Conventionally, a color printer often has two color conversion paths. One of the two color conversion paths (a path 1) is used when a color signal inputted is a chromatic color. The path 1 has a role of converting color signals inputted (e.g., RGB signals) into color signals (CMYK) corresponding to a color material of the printer. The other of the two color conversion parameters (a path 2) is a path used only when a color signal inputted is a substantially achromatic color. The path 2 is a path for converting a color inputted such that the color is reproduced with only a black (K) color material of the printer.
Effects of the path 2 will be explained using FIGS. 18 and 19.
FIG. 18 is a color conversion result by the path 1 when a character of a 50% achromatic color (R=G=G=50%) is inputted. The color conversion result is, for example, C=20%, M=10%, Y=10%, and K=30%. These colors are printed by an image forming unit 803. However, since the image forming unit 803 usually has some output position deviation, which is a mechanical instability element, respective data of CMYK are not always outputted to an identical position. In other words, an output result shown in FIG. 19 may be obtained. In this case, in a contour portion of a character outputted, color blurring occurs to deteriorate an image quality.
FIGS. 20 and 21 are diagrams for explaining color conversion processing by the path 2 in the case in which the character of the same 50% achromatic color is inputted. As shown in FIG. 20, since a color conversion result by the path 2 is only the black (K) color material, even if positional deviation occurs in the image forming unit 803, blurring of a contour part of the character does not occur as shown in FIG. 21. Thus, deterioration in an image quality does not occur.
In this way, it is possible to perform color conversion without deteriorating an image quality by using the path 2 when a color signal inputted is a substantially achromatic color. Since the path 2 is effective only when an input is a substantially achromatic color, as shown in FIG. 17, a judging unit 901 is provided to perform processing by a color converting unit 902 using the path 1 when the color signal inputted is a chromatic color and perform processing by an achromatic color gradation adjusting unit 903 using the path 2 when the color signal inputted is an achromatic color.
The conventional color adjustment processing in such a constitution is, as shown in FIG. 22, performed by correcting a color conversion table used in the path 1 using a color conversion table adjusting unit 904.
However, the conventional color adjustment processing described above has the following problems.
FIG. 23 is a diagram showing a result of printing an image without performing the color adjustment processing as described above. FIG. 24 is a diagram indicating which image area is subjected to the color conversion processing by the path 1 and the path 2 in the image of the print result shown in FIG. 23.
As shown in the figures, even when an image including a color signal processed by the path 1 and the path 2 is inputted, since the color conversion table and a TRC (Tone Reproduction Curve) are adjusted in advance, as shown in FIG. 23, it is possible to print an image without a sense of incongruity even in a boundary of the path 1 and the path 2.
In such a state, when a user feels that a color printed (see FIG. 23) undesirable and desires to make the printed image more bright, the color conversion table adjusting unit 904 in the constitution of FIG. 22 is used to correct the conversion table to increase brightness the printed result or to change the color to a favorite color.
However, in the conventional constitution shown in FIG. 22, since the color conversion table of the path 1 is only corrected, in an output result after correcting the color conversion table (after the color adjustment processing), a boundary of processing for an image area subjected to color conversion by the path 2 and an image area subjected to color conversion by the path 1 (a path to which the color adjustment processing is applied) may appear, resulting in an unnatural print result.